Problem: In language class, the girl to boy ratio is $10$ to $7$. If there are a total of $68$ students, how many girls are there?
Explanation: A ratio of $10$ girls to $7$ boys means that a set of $17$ students will have $10$ girls and $7$ boys. A class of $68$ students has $4$ sets of $17$ students. Because we know that there are $10$ girls in each set of $17$ students, the class must have $4$ groups of $10$ girls each. There is a total of $40$ girls in language class.